There has been reported that fucoidan, which is a sulfated polysaccharide contained in brown algae (Phaeophyta), has various biological activities including anticoagulant, lipemia-clearing, antitumor, cancerous metastasis-inhibitory and anti-AIDS virus infection effects. Thus fucoidan is highly useful as a medicine.
When it is intended to use fucoidan as such as a medicine, however, there arise problems in antigenicity, uniformity, anticoagulant activity, etc., since fucoidan is a sulfated polysaccharide having an extremely large molecular weight. Accordingly, it is often needed to degrade fucoidan to a certain extent.
It has been therefore desired to clarify the structure of fucoidan and reveal the relation thereof with its biological activities. However, fucoidan is a high-molecular compound carrying many branched chains and various constituting sugars. Moreover, its sulfate groups are bonded to various positions. These characteristics make it highly difficult to analyze the structure of fucoidan. To analyze the structure of a polysaccharide, there is known a method comprising treating the polysaccharide with an enzyme capable of degrading the same and analyzing the structures of the oligosaccharides thus formed. However there has been commercially available neither any fucoidan degrading enzyme giving products with known sugar chain structure nor one serving as the standard of a fucoidan oligosaccharide from among those reported hitherto.
For these reasons, there have been required sugar compounds with identified structures, a polysaccharide degrading enzyme useful in the production of these sugar compounds and a microorganism useful in the production of the sugar compounds.
The present invention aims at providing sugar compounds usable in analyzing the structure of fucoidan, identifying enzymatically degraded products of fucoidan and detecting the biological activities thereof, a novel endo-fucoidan-lyase useful in studies on fucoidan such as the production of fucoidan oligosaccharides and a novel microorganism useful for producing the sugar compounds.
In short, the first invention of the present invention relates to sugar compounds represented by the following general formula (1) or (2), wherein at least one alcoholic hydroxyl group has been sulfated, or salts thereof: ##STR3## wherein X represents hydrogen or a group represented by the following formula (3): ##STR4## Y represents hydrogen or a group represented by the following formula (4) or (5): ##STR5## provided that X and Y are not hydrogen at the same time; and Z represents hydrogen or a group represented by the following formula (6): ##STR6##
Examples of the compounds represented by the above general formula (1) or (2) are those represented by the following general formulae (7) to (15): ##STR7##
The second invention of the present invention relates to an endo-fucoidan-lyase characterized by having the following physicochemical properties.
(I) Function: acting on fucoidan and thus liberating at least the compounds represented by the above formulae (7) and (8).
(II) Optimum pH value: ranging from pH 6 to 10.
(III) Optimum temperature: ranging from 30 to 40.degree. C.
The third invention of the present invention relates to a bacterium belonging to the genus Fucoidanobacter which is a novel microorganism useful in the production of the sugar compounds of the first invention of the present invention, having menaquinone in the electron transport chain and containing 60% of GC [mole percent guanine plus cytosine content (mol % G+C)].
In the formulae (1), (2), (4) to (15) and (17) to (25) given herein, ".about." means that mannose or galactose occurs as both of .alpha.- and .beta.-anomers.
The present inventors have found out that the sugar compounds of the present invention can be obtained by treating fucoidan with the enzyme of the second invention of the present invention or the cell extract or culture supernatant of the bacterium of the third invention of the present invention, thus completing the present invention.